As is well known, universally jointed drive lines are often used to transmit a torque from a power source to a load which is movable with respect to the power source. Since they are able to pivot or flex, while transmitting torque, universal joints are able to accommodate a variety of movements. However, in many cases, relative movements between the source and load require length changes as well as pivotal or angular movements in the drive line. These length changes have long been accommodated by sliding splined connections and the like at some point in the drive line. More recently, universal joints have been designed which permit relative axial movement between their driving and driven members, thus, in some cases, avoiding the need for sliding splined connections.
It is well known that a disadvantage of sliding or telescoping splined connections in drive lines is their high frictional resistance to telescoping under load. This can add greatly to the stresses on bearings and other members supporting the drive line. Another disadvantage of such splined connections is their "stick-slip" characteristic, due to differences between static and dynamic sliding friction, which often causes the splines to telescope in an abrupt or jerky manner and which makes them undesirable for many applications which require smoothness and quietness. Replacement of telescoping splines, where practical, with telescoping universal joints, i.e. joints allowing axial movement between their driving and driven members, greatly reduces these sliding spline problems. This is because telescoping universal joints are usually better lubricated internally than sliding splines, have their torque transmitting surfaces farther from the axis of rotation, are less likely to have static conditions and static friction between torque transmitting surfaces and, in many cases, substitute rolling or quasi-rolling action for sliding action at the torque transmitting surfaces.
Because of this functional superiority and because of simplification sometimes possible by eliminating sliding splines, telescoping universal joints have become common in certain applications. However, their use is limited to applications requiring a relatively small length change since their stroke is severely limited by the need to compromise pivotal angular capacity to achieve long strokes and by the difficulty in sealing a universal joint which combines a long stroke with its pivotal movement. Further, the usable stroke of such a joint is even less than that theoretically possible because the joint may come apart at the end of the theoretically possible stroke or because a functional part of the joint may strike some other member, causing noise, vibration and possible damage to the unit. Thus, a "margin of safety" is usually allowed at each end of the theoretical stroke to allow for these practical conditions.
An object of this invention is to provide a telescoping universal joint having stroke limiting means which are able to sustain substantial axial forces and impacts during normal joint operation and the engagement of which does not cause undesirable noise or vibration of the universal joint.
Telescoping universal joints incorporating such stroke limiting means have many more potential applications than present joints because: The full theoretical stroke of the joint can be used; multiple joints can be used in series to accommodate greater length changes; and telescoping joints can be used in conjunction with telescoping splines and similar structures to produce novel interaction in the drive line. This latter combination is particularly suitable for a class of applications which requires only a relatively small length change in the drive line during normal operation but which requires an additional provision for length changes to accommodate tolerances in the building of the machine, to permit assembly or disassembly of parts of the machine, or to accommodate occasional greater than normal length changes and the like. In these applications, a telescoping universal joint can accommodate normal length changes with low frictional resistance and little "stick-slip" tendency, while for greater length changes, the stroke limiting means of the joint prevents damage of disassembly of the universal joint and permits the excess stroke to be taken by sliding splines or other such mechanism in association with the universal joint. In many instances, a drive line will necessarily have splines or the like for other reasons and such splines can also be used to accommodate excess stroke.
Thus, telescoping universal joints and telescoping splines can be combined in a novel manner with little or no penalty, provided only that the universal joint incorporates stroke limiting means sufficiently strong and servicable to transmit the relatively large axial forces needed to cause splines or the like to slide when required. Automobile and truck drive shafts often fall into this class of applications.
Another object of this invention is to provide an alternative mechanical sealing means for telescoping universal joints for use in place of the flexible boot-type seals presently used.
Further objects of this invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.